Effects of body temperature maintenance on glucose, insulin, and corticosterone responses to acute hypoxia in the neonatal rat.

One of the biggest challenges of premature birth is acute hypoxia. Hypothermia during acute hypoxic periods may be beneficial. We hypothesized that prevention of hypothermia during neonatal hypoxia disrupts glucose homeostasis and places additional metabolic challenges on the neonate. Pups at PD2 and PD8 were exposed to 8% O2 for 3 h, during which they were allowed to either spontaneously cool or were kept isothermic. There was also a time control group that was subjected to normoxia and kept isothermic. Plasma glucose, insulin, C-peptide, corticosterone, and catecholamines were measured from samples collected at baseline, 1 h, 2 h, and 3 h. In postnatal day 2 (PD2) rats, hypoxia alone resulted in no change in plasma glucose by 1 h, an increase by 2 h, and a subsequent decrease below baseline values by 3 h. Hypoxia with isothermia in PD2 rats elicited a large increase in plasma insulin at 1 h. In PD8 rats, hypoxia with isothermia resulted in an initial increase in plasma glucose, but by 3 h, glucose had decreased significantly to below baseline levels. Hypoxia with and without isothermia elicited an increase in plasma corticosterone at both ages and an increase in plasma epinephrine in PD8 rats. We conclude that the insulin response to hypoxia in PD8 rats is associated with an increase in glucose similar to an adult; however, insulin responses to hypoxia in PD2 rats were driven by something other than glucose. Prevention of hypothermia during hypoxia further disrupts glucose homeostasis and increases metabolic challenges.